Why Does My JavaScript Code Assign Instead of Comparing?

Understanding Equality Comparison in JavaScript

In JavaScript, equality comparison is often a source of confusion, particularly when using the single equals sign (=). Let's delve into the reason why the code snippet provided in the original question doesn't behave as expected.

The Role of Assignment

The single equals sign (=) is used for assignment, not equality comparison. As a result, when you write:

if (str = '')

you're actually assigning an empty string to the variable 'str' instead of checking its value for equality.

Equality Comparison Operators

To compare values for equality in JavaScript, you should use the double equals sign (==) for loose comparison (allowing for type coercion) or the triple equals sign (===) for strict comparison (without type coercion).

Revisiting the Code

Replacing the single equals sign with double or triple equals will ensure that the desired comparison is performed:

if (str === '') {
    console.log("The string cannot be blank");
} else if (str.length <= 9) {
    console.log("The string must be at least 9 characters long");
} else if (str.length <= 10) {
    console.log("The string is long enough.");
}

Explanation of the Correction

Using === (strict comparison) in this case guarantees that the value of 'str' is compared with an empty string, avoiding the assignment error. As a result, the code will accurately determine if the string is blank, has a length less than or equal to 9, or has a length up to 10.

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